Bob ,
European cities tend to be much more densely populated. In fact, one of the things I don't like about the US is that, with some notable exceptions like New York, San Francisco and a few others, there is too much suburban sprawl, which forces you to be car-dependant. A lot of it is to do with silly zoning rules, which prevent the mixing of commercial and residential, forcing you to drive 15 minutes just to buy a pint of milk. This channel has quite a few interesting videos about it:
If my partner didn't need it for a job outside the city, we would probably not even have a car. And if my commute were shorter I would not be considering a Vespa but I'd rely on my ebike only.
Also in Europe driving tests and regulation in general tend to be much stricter, for both cars and motorcycles. We don't let a 16-year old ride an R1, they need to be 24 (or 21 with prior experience). The argument that US roads are wider so rules don't need to be much stricter doesn't hold much water, because, even normalising by miles driven, US roads remain much more dangerous than in Western Europe, especially than in the UK.
All of this to say that the importance of speed limits in many European cities, with narrower roads and a much greater population density, is quite different from most of the US.
Specifically on 20mph: it is a contentious point, because these limits certainly make sense near schools or in narrower roads. I am not convinced they make wider roads safer, though.
This UK government study concluded that:
Quote:
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/757307/20mph-headline-report.pdf
based on the evidence available to date, this study has found no significant change in collisions and casualties, in the short term, in the majority of the case study areas (including the aggregated set of residential case studies). While some individual case study areas show a reduction in collisions / casualties when background trends are accounted for, these results are based on very small sample sizes and it is not possible to attach any confidence to their significance.
This article also mentions inconclusive results:
https://www.itsinternational.com/its2/feature/speed-limits-20-really-plenty
as does this British one:
https://www.qub.ac.uk/News/Allnews/featured-research/20-mph-speed-limits-little-impact-crashes.html
However, like many things, it has become a culture war between green zealots who think no one should ever drive, and petrolheads who think it's their constitutional right to drive stupidly dangerous and polluting vehicles everywhere. There is very little room for sensible voices in between.
Ah, one thing that seems interesting and I'd like to understand more is if 20mph reduce pollution and fuel consumption by keeping vehicles at a more constant speed, preventing them from accelerating too much; after all, even if you reach 30mph in a city, you won't keep that speed for long.
A counterargument is that 20mph don't make much practical difference during the day and rush hour, but they make a difference when roads are emptier (like at night or during certain holidays) and there is little reason to penalise vans and other vehicles who need to drive at those times; for a van crossing the entire city at night, 20mph instead of 30mph can increase the journey time quite a bit.